I love this message! It's been in my favourites ever since you posted it, but only now have I thought to post a decent comment, lol
It's such a terrible thing that up until recently - in this day and age - that not everyone could donate blood, purely because of something as inconsequential and harmless as having your own emotions. At MA said in her comment, this is a real step forward in equal rights.
I like how you've picked out the red in the pride flag, as it mirrors blood, and the same goes for the title ( the ' sneaky fourth line ' ). Putting so much, so cleverly in just three ( or four, considering the title ) lines is really wonderful.
Anyway, aside from my ranting and ravings, glad you posted this, and that it happened in the first place!